Penetration type screen for screen golf

ABSTRACT

A penetration type screen for screen golf is provided. A golf ball struck by a golfer is allowed to penetrate through the screen such that the struck golf ball disappears from view, thereby increasing the pleasance of golfing environments and a flying image of the golf ball is allowed to be displayed in the simulation image as the struck golf ball disappears from view, thereby further improving the realism of virtual golf, and wherein screen elements which constitute the penetration type screen are prevented from being opened even when golf balls repeatedly pass between the screen elements, thereby improving product reliability. To accomplish this, the penetration type screen includes a plurality of screen elements, each being formed of spandex, the plurality of screen elements being arranged side by side such that the screen elements at least partially overlap each other and are each inclined at a specific angle.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a Continuation Application of 14/130,933 filed Jan. 6, 2014, which is a National Stage Application of PCT International Patent Application No. PCT/KR2012/005365 filed Jul. 6, 2012, which claims priority to Korean Patent Application No. 10-2011-0066859 filed Jul. 6, 2011, which are all hereby incorporated by reference in their entirety.

BACKGROUND

The present invention relates to a penetration type screen for screen golf, and more particularly to a penetration type screen used for so-called screen golf which uses a virtual golf simulation apparatus that allows golfers to play golf through virtual golf images projected onto a screen.

As the interest in golf has recently increased, a virtual golf simulation system, which is called “screen golf” and which provides realism allowing users to enjoy golf games indoor as though they play golf games on actual golf courses, has been introduced.

The virtual golf simulation system is implemented such that the system provides, as virtual reality, the same images as those of actual golf courses in order to provide realism allowing golfers to enjoy golf as though they play golf games on actual golf courses and also provides realistic moving golf ball images.

Specifically, an image provided by the golf simulation apparatus is projected onto a screen provided at a front side of a screen golf booth that forms a specific size of space such that a golfer can enjoy screen golf by striking a golf ball toward the screen while viewing the image projected onto the screen.

However, in the conventional screen golf system, golf balls struck by the golfer are spread in a messy way over the floor of the booth in which the screen golf system is installed, deteriorating user satisfaction associated with golfing environments.

Accordingly, there is a need to develop technology which allows a golf ball to disappear from view after the golf ball is struck such that the booth in which the screen golf system is installed is kept tidy to provide pleasant golfing environments and which also further improves the realism of virtual golf as the struck golf disappears from view.

SUMMARY

It is an object of the present invention to provide a penetration type screen for screen golf, wherein a golf ball struck by a golfer is allowed to penetrate through the screen such that the struck golf ball disappears from view, thereby increasing the pleasance of golfing environments and a flying image of the golf ball is allowed to be displayed in the simulation image as the struck golf ball disappears from view, thereby further improving the realism of virtual golf, and wherein screen elements which constitute the penetration type screen are prevented from being opened even when golf balls repeatedly pass between the screen elements, thereby improving product reliability.

In accordance with one embodiment of the present invention, the above and other objects can be accomplished by the provision of a penetration type screen for screen golf, the penetration type screen including a plurality of screen elements, each being formed of spandex, the plurality of screen elements being arranged side by side such that the plurality of screen elements at least partially overlap each other and are each inclined at a specific angle.

Preferably, each of the plurality of screen elements is formed of a fire-retardant-processed spandex material.

Preferably, the plurality of screen elements is arranged such that light of a projector for projecting an image is directed toward side surfaces of overlapping portions of the screen elements.

Preferably, the penetration type screen further includes a frame that supports the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle.

Preferably, the frame includes a support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle.

Preferably, the support guide portion includes an inclined surface portion such that an inclined surface of each of the plurality of screen elements is secured to and supported by the inclined surface portion, and a riser that is formed between the inclined surface portion and another inclined surface portion.

Preferably, the frame includes a first frame portion arranged at a front side of the plurality of screen elements, and a second frame portion corresponding to the first frame portion, the second frame portion being arranged at a rear side of the plurality of screen elements and being coupled to the first frame portion to support the plurality of screen elements.

Preferably, a first support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle is formed on the first frame portion and a second support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle is formed on the second frame portion, and the first frame portion and the second frame portion are coupled to each other such that the first support guide portion and the second support guide portion support the arrangement of the plurality of screen elements.

Preferably, the first support guide portion includes a first inclined surface portion such that an inclined front surface of each of the plurality of screen elements is secured to and supported by the first inclined surface portion, and a first riser that is formed at an end portion of the first inclined surface portion such that one side surface of each of the plurality of screen elements is secured to and supported by the first riser, and the second support guide portion includes a second inclined surface portion such that an inclined rear surface of each of the plurality of screen elements is secured to and supported by the second inclined surface portion, and a second riser that is formed at an end portion of the second inclined surface portion such that another side surface of each of the plurality of screen elements is secured to and supported by the second riser.

Preferably, the frame is constructed by coupling a plurality of sub-frames, each being provided to support part of the plurality of screen elements.

Preferably, each of the sub-frames includes a first sub-frame portion arranged at a front side of the plurality of screen elements, and a second sub-frame portion corresponding to the first sub-frame portion, the second sub-frame portion being arranged at a rear side of the plurality of screen elements and being coupled to the first sub-frame portion to support the plurality of screen elements.

Preferably, a first support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle is formed on the first sub-frame portion and a second support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle is formed on the second sub-frame portion, and the first sub-frame portion and the second sub-frame portion are coupled to each other such that the first support guide portion and the second support guide portion support the arrangement of the plurality of screen elements.

Preferably, an end portion of the first sub-frame portion of the sub-frame and an end portion of the second sub-frame portion of another sub-frame are arranged respectively at front and rear sides of a screen element, facing each other, such that the end portion of the first sub-frame portion and the end portion of the second sub-frame portion are coupled to each other.

A penetration type screen for screen golf according to the present invention has advantageous effects that a golf ball struck by a golfer is allowed to penetrate through the screen such that the struck golf ball disappears from view, thereby increasing the pleasance of golfing environments and a flying image of the golf ball is allowed to be displayed in the simulation image as the struck golf ball disappears from view, thereby further improving the realism of virtual golf. In addition, screen elements which constitute the penetration type screen are prevented from being opened even when golf balls repeatedly pass between the screen elements, thereby improving product reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary screen golf system including a penetration type screen according to the present invention;

FIG. 2 illustrates a penetration type screen for screen golf according to an embodiment of the present invention;

FIG. 3 illustrates the appearance of a desirable arrangement of a plurality of screen elements of a penetration type screen for screen golf according to an embodiment of the present invention;

FIG. 4 illustrates the appearance of an undesirable arrangement of the plurality of screen elements;

FIG. 5 illustrates an example in which a support guide portion formed on a frame supports the arrangement of the plurality of screen elements;

FIG. 6 is a cross-sectional view of sub-frames shown in FIG. 1 taken along line I-I in FIG. 1;

FIG. 7 is an exploded view of the sub-frames shown in FIG. 6;

FIG. 8 is a perspective view of the sub-frames shown in FIG. 7; and

FIG. 9 illustrates a penetration type screen for screen golf according to another embodiment of the present invention.

DETAILED DESCRIPTION

An embodiment of a penetration type screen for screen golf according to the present invention will now be described in more detail with reference to the accompanying drawings.

First, a screen golf system including a penetration type screen according to the present invention is schematically described as follows with reference to FIG. 1.

As shown in FIG. 1, the screen golf system is installed in a screen golf booth 1 having a specific size of space defined by side walls.

A penetration type screen S is attached to a front side of the screen golf booth 1 and a projector 210 that is operated by a golf simulator 200 is provided to project a virtual golf simulation image including a golf course, a background, a moving image of a golf ball, and the like onto the penetration type screen S.

If a golfer steps up to a swing plate 100 provided at the bottom of the booth 1 and strikes a golf ball placed on a golf mat 110 with a golf club, the struck golf ball flies toward the penetration type screen S. The golf ball penetrates through the penetration type screen S. Movement of the struck golf ball is detected by a sensor 220 and the golf simulator 200 implements the detected movement of the struck golf ball as an image and projects the image on the penetration type screen S through the projector 210.

The penetration type screen S is basically formed of a plurality of screen elements that are arranged side by side and is implemented such that the struck golf ball passes between screen elements.

A buffer is provided at a rear side of the penetration type screen S such that the penetrated golf ball is buffered and drops to a floor of the screen golf booth 1. The golf ball which has dropped to the floor of the screen golf booth 1 may be conveyed and provided back to the swing plate 100 through a ball conveyor (not shown) provided inside the screen golf booth 1.

The penetration type screen S is described below in more detail with reference to FIGS. 2 to 7.

As shown in FIG. 2, the penetration type screen S for screen golf according to an embodiment of the present invention is formed of a plurality of screen elements 10 arranged side by side.

Two frames 20 are provided respectively at upper and lower end portions of the plurality of screen elements 10 so as to support the array of screen elements 10.

Each of the frames 20 may be provided as a single integrated frame that supports the entirety of the plurality of screen elements 10 and may also be provided as a plurality of sub-frames 21, 22, and 23 into which the frame 20 is divided as shown in FIG. 2.

In the case in which the frame 20 is divided into a plurality of sub-frames (such as sub-frames 21, 22, and 23) such that each of the sub-frames 21 supports partial screen elements (where a combination of the sub-frame and the partial screen elements supported by the sub-frame is referred to as a “sub-penetration-type screen”), the penetration type screen may be configured by arranging a plurality of sub-penetration-type screens side by side such that, when part of the penetration type screen has a problem or needs to be washed, it is possible to separate and replace a sub-penetration-type screen corresponding to the part, achieving ease of work.

On the other hand, a conventional penetration type screen is configured by arranging a plurality of slats side by side, forming gaps between the slats through which a golf ball can pass. The conventional penetration type screen has a problem in that, as golf balls repeatedly pass through the gaps between the slats, the sizes of the gaps are gradually increased, deteriorating the external appearance, and also has a problem in that an image is not properly projected on the penetration type screen due to the increased sizes of the gaps.

The penetration type screen S according to the present invention is characterized in that the screen elements 10 are arranged side by side such that the screen elements 10 at least partially overlap each other and are each inclined at a specific angle.

That is, the screen elements 10 are mounted, overlapping each other, such that a part of one screen element 10-1 overlaps a part of another screen element 10-2 and a part of the screen element 10-2 overlaps a part of another screen element 10-3 as shown in FIG. 3. Here, each screen element 10 is mounted inclined at a specific angle.

It is preferable that the overlapping portion of each of the screen elements 10 not exceed a half of one screen element and that portions of the screen elements 10, each of which is smaller than a half of one screen element, overlap each other.

FIG. 3 is a cross-sectional view of the arranged screen elements shown in FIG. 2 taken along line I-I in FIG. 2. In FIG. 3, illustration of the frame part is omitted.

It is preferable that, as shown in FIG. 3, the direction of light of the projector 210 be taken into consideration when the plurality of screen elements 10 is arranged (or installed) such that the screen elements 10 overlap each other and are each inclined at a specific angle.

That is, when the projector 210 projects an image obliquely from one side as shown in FIG. 1, light of the projector 210 travels obliquely toward the penetration type screen as shown in FIG. 3.

Here, if each of a plurality of screen elements is arranged to be inclined such that a front surface of the screen element faces incident light from the projector as shown in FIG. 4, shadows D are created by light from the projector such that thick stripes are viewed over the entirety of the penetration type screen, which may cause simulation images not to be smoothly viewed.

Accordingly, it is possible to prevent shadows from being created by light from the projector by arranging (or installing) the screen elements such that light of the projector is directed toward side surfaces of the overlapping portions of the screen elements as shown in FIG. 3.

In addition, by arranging the screen elements such that the screen elements overlaps each other, taking into consideration the direction of light of the projector as shown in FIG. 3, it is possible to significantly reduce the thicknesses of stripes viewed on the penetration type screen and to allow the stripes to appear uniform, thereby allowing the user not to feel visual discomfort.

If a golf ball is struck toward the penetration type screen in which the plurality of screen elements is arranged such that the screen elements overlap each other and are each inclined at a specific angle, the struck golf ball passes through the penetration type screen while opening an overlapping portion of screen elements. The opened screen elements immediately return to the original state. Here, since each of the screen elements is formed of spandex, the screen elements can elastically return to an original state and can easily be kept in the original shape even when a golf ball repeatedly passes through the screen elements.

Conventionally, elasticity is given to a plurality of slats, which are arranged side by side to constitute a penetration type screen, by manufacturing each of the slats using non-elastic cloth and providing a number of means for providing elasticity to end portions of the slats. However, since the slats are lacking in elasticity, there is a problem in that it is not possible to prevent the sizes of the gaps between slats from being easily increased as golf balls repeatedly pass between the slats over a long period of time and there is also a risk that the portions of the slats, which are formed of cloth, may be separated from the portions thereof which provide elasticity.

The penetration type screen according to the present invention overcomes such problems by forming each of the plurality of screen elements of spandex and improves stability (or reliability) by performing fire retardant processing on the spandex material to prevent the spandex material from burning.

Specifically, after fire retardant processing is performed on spandex thread, the fire-retardant-processed spandex thread and fire-retardant-processed silicon may be used to manufacture each screen element or may be used to manufacture a single large screen and then to cut the single large screen into screen elements.

On the other hand, as golf balls repeatedly pass between the plurality of screen elements 10 which are arranged such that each screen element overlap each other and are each inclined at a specific angle as shown in FIG. 3, the overlapping state of each screen element may not be maintained.

For example, as golf balls repeatedly pass between the plurality of screen elements over a long period of time, a part of one screen element which should overlap another screen element such that the part of the one screen element is located behind the other screen element may be wrongly arranged in front of the other screen element, which may cause the screen elements to be viewed as being partially dislocated when viewed over the entire penetration type screen.

Accordingly, it is more preferable that a component for performing a function to maintain the arrangement of the plurality of screen elements in which the screen elements overlap each other and are each inclined at a specific angle be provided. FIGS. 5 to 8 illustrate an example in which such a function is performed through a frame that supports the arrangement of the plurality of screen elements.

FIG. 5 illustrates an example in which a support guide portion supports the arrangement of the plurality of screen elements and FIG. 6 is a cross-sectional view of the sub-frames 21, 22, and 23 shown in FIG. 1 taken along line I-I in FIG. 1.

FIG. 7 is an exploded view of the sub-frames 21, 22, and 23 shown in FIG. 6 and FIG. 8 is a perspective view of the sub-frames shown in FIG. 7.

As shown in FIGS. 5 to 8, it is preferable that support guide portions 31 and 32 be formed on the frame 20 so as to support the arrangement of the plurality of screen elements 10 in which the screen elements 10 overlap each other and are each inclined at a specific angle.

Each of the support guide portions 31 and 32 is formed in a shape corresponding to the arrangement of the plurality of screen elements 10, in which the screen elements 10 overlap each other and are each inclined at a specific angle, so as to allow the arrangement of the plurality of screen elements 10 to be maintained.

That is, the support guide portions 31 and 32 provide supporting force to allow the screen elements to quickly return to the original state when a golf ball penetrates through the screen elements.

As shown in FIG. 5, the frame 20 may include a first frame portion 20-1 which is arranged at a front side of the plurality of screen elements 10 and a second frame portion 20-2 which corresponds to the first frame portion 20-1 and is arranged at a rear side of the plurality of screen elements 10 and is coupled to the first frame portion 20-1 to support the plurality of screen elements 10.

That is, the frame 20 may be constructed by coupling the first frame portion 20-1 and the second frame portion 20-2 to each other so as to support all screen elements.

A first support guide portion 31 having a shape corresponding to the arrangement of the plurality of screen elements 10, in which the screen elements 10 overlap each other and are each inclined at a specific angle, may be formed on the first frame portion 20-1 and a second support guide portion 32 having a shape corresponding to the arrangement of the plurality of screen elements 10, in which the screen elements 10 overlap each other and are each inclined at a specific angle, may be formed on the second frame portion 20-2 and the first frame portion 20-1 and the second frame portion 20-2 may be coupled to each other to allow the first support guide portion 31 and the second support guide portion 32 to support the arrangement of the plurality of screen elements 10.

FIG. 6 illustrates a state in which the frame 20 is constructed by coupling a plurality of sub-frames 21, 22, and 23 to each other. As shown in FIG. 7, it is preferable that the sub-frames 21, 22, and 23 respectively include first sub-frame portions 21-1, 22-1, and 23-1, which are arranged at a front side of the plurality of screen elements 10, and second sub-frame portions 21-2, 22-2, and 23-2 which correspond respectively to the first sub-frame portions 21-1, 22-1, and 23-1 and which are arranged at a rear side of the plurality of screen elements 10 such that the second sub-frame portions 21-2, 22-2, and 23-2 are coupled to the first sub-frame portions 21-1, 22-1, and 23-1 to support the plurality of screen elements 10.

As shown in FIGS. 6 and 7, an end portion X of a first sub-frame portion 21-1 of one sub-frame 21 and an end portion Y of a second sub-frame portion 22-2 of another sub-frame 22 may be arranged respectively at the front and rear sides of the screen elements 10, facing each other, such that the end portion X of the first sub-frame portion 21-1 and the end portion Y of the second sub-frame portion 22-2 are coupled to each other.

In the same manner, an end portion X of a first sub-frame portion 22-1 of the sub-frame 22 and an end portion Y of a second sub-frame portion 23-2 of another sub-frame 23 may be arranged respectively at the front and rear sides of the screen elements 10, facing each other, such that the end portion X of the first sub-frame portion 22-1 and the end portion Y of the second sub-frame portion 23-2 are coupled to each other.

Accordingly, there are advantages in that it is possible to configure the sub-frames such as the sub-frame 21 so as to continuously support the screen elements 10 without discontinuous portions between the sub-frames while enabling simple assembly of the sub-frames.

Here, it is preferable that, as shown in FIGS. 7 and 8, a first support guide portion 31 having a shape corresponding to the arrangement of the plurality of screen elements, in which the screen elements overlap each other and are each inclined at a specific angle, be formed on the first sub-frame portions 21-1, 22-1, and 23-1 and a second support guide portion 32 having a shape corresponding to the arrangement of the plurality of screen elements, in which the screen elements overlap each other and are each inclined at a specific angle, be formed on the second sub-frame portions 21-2, 22-2, and 23-2 and the first sub-frame portions 21-1, 22-1, and 23-1 and the second sub-frame portions 21-2, 22-2, and 23-2 may be coupled to each other to allow the first support guide portion 31 and the second support guide portion 32 to support the arrangement of the plurality of screen elements.

In addition, it is preferable that, as shown in FIG. 8( a), the first support guide portion 31 include first inclined surface portions 31 a such that inclined front surfaces of the plurality of screen elements 10 are secured to and supported by the first inclined surface portions 31 a, and first risers 31 b which are formed at end portions of the first inclined surface portions 31 a such that one side surfaces of the screen elements are secured to and supported by the first risers 31 b.

It is also preferable that, as shown in FIG. 8( b), the second support guide portion 32 include second inclined surface portions 32 a such that inclined rear surfaces of the plurality of screen elements 10 are secured to and supported by the second inclined surface portions 32 a, and second risers 32 b which are formed at end portions of the second inclined surface portions 32 a such that the other side surfaces of the screen elements are secured to and supported by the second risers 32 b.

Accordingly, the structure of the first support guide portion 31 including the first inclined surface portions 31 a and the first risers 31 b and the structure of the second support guide portion 32 including the second inclined surface portions 32 a and the second risers 32 b are coupled to each other to form the structure in which the screen elements 10 overlap each other and are each inclined at a specific angle.

FIG. 9 illustrates a state in which a plurality of support members 40 is arranged at specific intervals at the rear sides of the plurality of screen elements 10 such that the plurality of support members 40 crosses the plurality of screen elements 10.

It is preferable that the support members 40 be formed of a highly elastic substance such as spandex or rubber. Both end portions of the support members 40 may be fixed to wall surfaces or alternatively additional structures may be provided such that the support members 40 are fixed to the structures.

Accordingly, the support members 40 support the plurality of screen elements such that the screen elements can return to the original shapes even when golf balls pass between the screen elements.

Various embodiments of the present invention have been described in the best mode.

The penetration type screen for screen golf according to the present invention can be used in industries related to a so-called Screen Golf for a user to be able to play a virtual golf round by golf simulation based on a virtual reality. 

What is claimed is:
 1. A penetration type screen for screen golf, the penetration type screen comprising: a plurality of screen elements, each being formed of spandex, the plurality of screen elements being arranged side by side such that the plurality of screen elements at least partially overlap each other and are each inclined at a specific angle.
 2. The penetration type screen according to claim 1, wherein each of the plurality of screen elements is formed of a fire-retardant-processed spandex material.
 3. The penetration type screen according to claim 1, wherein the plurality of screen elements is arranged such that light of a projector for projecting an image is directed toward side surfaces of overlapping portions of the screen elements.
 4. The penetration type screen according to claim 1, further comprising a frame that supports the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle.
 5. The penetration type screen according to claim 4, wherein the frame includes a support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle.
 6. The penetration type screen according to claim 5, wherein the support guide portion includes: an inclined surface portion such that an inclined surface of each of the plurality of screen elements is secured to and supported by the inclined surface portion; and a riser that is formed between the inclined surface portion and another inclined surface portion.
 7. The penetration type screen according to claim 4, wherein the frame includes: a first frame portion arranged at a front side of the plurality of screen elements; and a second frame portion corresponding to the first frame portion, the second frame portion being arranged at a rear side of the plurality of screen elements and being coupled to the first frame portion to support the plurality of screen elements.
 8. The penetration type screen according to claim 7, wherein a first support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle is formed on the first frame portion and a second support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle is formed on the second frame portion, and the first frame portion and the second frame portion are coupled to each other such that the first support guide portion and the second support guide portion support the arrangement of the plurality of screen elements.
 9. The penetration type screen according to claim 8, wherein the first support guide portion includes: a first inclined surface portion such that an inclined front surface of each of the plurality of screen elements is secured to and supported by the first inclined surface portion; and a first riser that is formed at an end portion of the first inclined surface portion such that one side surface of each of the plurality of screen elements is secured to and supported by the first riser, and the second support guide portion includes: a second inclined surface portion such that an inclined rear surface of each of the plurality of screen elements is secured to and supported by the second inclined surface portion; and a second riser that is formed at an end portion of the second inclined surface portion such that another side surface of each of the plurality of screen elements is secured to and supported by the second riser.
 10. The penetration type screen according to claim 4, wherein the frame is constructed by coupling a plurality of sub-frames, each being provided to support part of the plurality of screen elements.
 11. The penetration type screen according to claim 10, wherein each of the sub-frames includes: a first sub-frame portion arranged at a front side of the plurality of screen elements; and a second sub-frame portion corresponding to the first sub-frame portion, the second sub-frame portion being arranged at a rear side of the plurality of screen elements and being coupled to the first sub-frame portion to support the plurality of screen elements.
 12. The penetration type screen according to claim 11, wherein a first support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle is formed on the first sub-frame portion and a second support guide portion having a shape corresponding to the arrangement of the plurality of screen elements in which the plurality of screen elements overlap each other and are each inclined at a specific angle is formed on the second sub-frame portion, and the first sub-frame portion and the second sub-frame portion are coupled to each other such that the first support guide portion and the second support guide portion support the arrangement of the plurality of screen elements.
 13. The penetration type screen according to claim 11, wherein an end portion of the first sub-frame portion of the sub-frame and an end portion of the second sub-frame portion of another sub-frame are arranged respectively at front and rear sides of a screen element, facing each other, such that the end portion of the first sub-frame portion and the end portion of the second sub-frame portion are coupled to each other. 